Question

In a A.C. generator voltage dip occurs in 2 stages

Sketch a voltage time graph showing the pattern of voltage dip

Referring to this graph state with reason the effect on the electrical system of a small power installation when large load is suddenly switched on.

Explain each of the following categories of voltage control.

Error operated.

Functional.

The voltage of an unregulated a.c. generator can vary 30% or more from no load to full load, when sudden load is connected. The out put voltage changes, due to internal voltage dip in generator winding.

In a regulated AVR. AVR will control the generator's voltage to ±2.5% (or better) of its set value over the full load range. This is its steady-state voltage regulation.

Transient voltage dip is usually limited to 15% for a specified sudden load change with recovery back to rated voltage within 1.5 seconds because AVR increases the field current to restore voltage.

The voltage dip can cause light to dim and may affect electronic equipment

Can slow down or stall the running motor and affect the under voltage devices.

Error operated.

Measures output voltage and compares to reference.

The function of error operated type AVR is to maintain the terminal voltage of the generator within acceptable limit under steady load and transient load condition

Functional.

The load current causes the voltage to change

The load current is used to alter the excitation as load increases.